The problem of switching the heating water circuit between two flow paths, specifically once through a heating circuit in the building and once through a heat exchanger for heating service water, arises in heating facilities, in particular compact heating facilities. For this, it is known to apply pump assemblies with integrated valve elements which switch between two possible flow paths, in dependence on the rotation direction of the impeller of the pump assembly. As a rule, a movable valve element is provided for this, and this valve element is carried along by the flow around the impeller, and, depending on the flow direction, is pressed against one of two possible exits, in order to close these, so that the flow leaves through the respective other exit of the pump assembly. This means that the valve element closes the exits in an alternating manner such that one exit is always closed and the other exit is simultaneously opened. Water hammers which lead to undesirable noises in the system are a problem with such designs.